Method and apparatus for competition-based transmitting of uplink data in wireless communication system to which non-orthogonal multiple access scheme is applied

ABSTRACT

Provided are a method and an apparatus for competition-based transmitting of uplink data in a wireless communication system to which a non-orthogonal multiple access scheme is applied. Particularly, a terminal receives, from a base station, information relating to a predefined codeword for non-orthogonal multiple access. The predefined codeword includes a first spreading code and a second spreading code. The terminal configures a base layer using the first spreading code and configures an enhancement layer using the second spreading code. The terminal transmits a terminal identifier and data to the base station through a competition-based resource which overlappingly uses the base layer and the enhancement layer, wherein the terminal identifier is transmitted through the base layer and the data is transmitted through the enhancement layer.

BACKGROUND OF THE INVENTION Cross-Reference to Related Applications

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2017/004352, filed on Apr. 25, 2017,which claims the benefit of U.S. Provisional Application No. 62/340,465,filed on May 23, 2016, the contents of which are all hereby incorporatedby reference herein in their entirety.

Field of the Invention

The present specification relates to wireless communication, and moreparticularly, to a method and apparatus for contention-basedtransmission of uplink data in a wireless communication system to whicha non-orthogonal multiple access scheme is applied.

Related Art

A wireless communication system is widely deployed to provide varioustypes of communication services, such as voice and data. An object of awireless communication system is to enable a plurality of UEs to performreliable communication regardless of their locations and mobility.

In general, a wireless communication system is a multiple access systemcapable of supporting communication with a plurality of UEs by sharingavailable radio resources. Examples of radio resources include time, afrequency, code, transmission power and so on. Examples of a multipleaccess system includes a time division multiple access (TDMA) system, acode division multiple access (CDMA) system, a frequency divisionmultiple access (FDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system and so on.

A requirement of a next-generation wireless communication system is toaccommodate significantly explosive data traffic, to increase a dramaticincrease in a transfer rate per user, to accommodate the significantlyincreased number of connected devices, and to support a very lowend-to-end (E2E) latency and high energy efficiency. For this, there isongoing research on various techniques such as dual connectivity,massive multiple input multiple output (MIMO), in-band full duplex,non-orthogonal multiple access (NOMA), super wideband support, devicenetworking, or the like.

SUMMARY OF THE INVENTION

The present specification proposes a method and apparatus forcontention-based transmission of uplink data in a wireless communicationsystem to which a non-orthogonal multiple access scheme is applied.

The present specification proposes a method and apparatus fortransmitting uplink data in a contention-based manner in a wirelesscommunication system to which a non-orthogonal multiple access scheme isapplied.

The apparatus includes a radio frequency (RF) unit transmitting andreceiving a radio signal, and a processor operatively coupled to the RFunit.

First, a contention-based resource may correspond to a resource regionfor contention-based uplink connection or uplink data transmission onthe basis of non-orthogonal multiple access

A user equipment (UE) receives, from a base station, informationregarding a pre-defined codeword for non-orthogonal multiple access. Thepre-defined codeword includes a first spreading code and a secondspreading code. The pre-defined codeword may correspond to all codewordsincluded in a codebook pre-defined between the base station and the UE.Therefore, both of the first spreading code and the second spreadingcode may correspond to the codeword.

The UE configures a base layer by using the first spreading code, andconfigures an enhancement layer by using the second spreading code.

The UE transmits a UE identification and data to the base stationthrough a contention-based resource which uses the base layer and theenhancement layer in a superposed manner. In this case, the UEidentification is transmitted through the base layer, and the data istransmitted through the enhancement layer. In addition, the UEidentification and the data are transmitted through the same datachannel. The UE identification and the data may be transmitted only withthe data channel without having to distinguish a control channel and thedata channel, each of which has different reliability.

That is, in the present embodiment, one user (or UE) performscontention-based transmission by superposing two layers (a base layerand an enhancement layer) in a wireless communication system to which anon-orthogonal multiple access scheme is applied. Since the base layerand the enhancement layer are identified with a codeword, acontention-based resource may be identified with the base layer and theenhancement layer according to the codeword.

The base station may perform multi-user detection (MUD) for the data andthe UE identification transmitted by the UE. If the base stationsucceeds in detection of the UE identification and fails in detection ofthe data, the UE may receive a retransmission request for the data fromthe base station. Since detection of the UE identification issuccessful, the base station can recognize which UE transmits the data,and thus data retransmission can be requested to a corresponding UE. TheUE may retransmit the data to the base station through the enhancementlayer. In this case, the UE identification and the data retransmittedfrom the UE may be decoded by being combined to each other. Withouthaving to retransmit the UE identification, the base station may decodethe UE identification by combining the retransmitted data and the UEidentification previously transmitted through the base layer.

In addition, the UE may transmit a reference signal for channelestimation to the base station. In this case, the number of referencesignals is less than the number of pre-defined codewords. In addition,it may be configured such that the base layer and enhancement layerwhich are used in a superposed manner may correspond to one referencesignal. The reference signal may correspond to a DMRS.

Conventionally, since contention-based data transmitted from multipleusers is identified with the DMRS, it has been meaningless even if thenumber of codewords is greater than the number of DMRSs. However, if thebase layer and enhancement layer for one user are tied to one DMRS, twocodewords can be used with one DMRS. Therefore, even if the number ofcodewords is greater than the number of DMRSs, it is possible toidentify more layers than the number of DMRSs.

In addition, the UE may receive power allocation information for thebase layer and the enhancement layer from the base station through radioresource control (RRC) signaling, high layer signaling, or commoncontrol information. Accordingly, the base station performs channelequalization on the basis of the power allocation information for eachlayer.

A code rate for the base layer and a code rate for the enhancement layermay be designated according to a codeword index of the predefinedcodeword. Alternatively, modulation and coding scheme (MCS) for the baselayer and MCS for the enhancement layer may be designated according tothe codeword index of the predefined codeword.

That is, a relation between the codeword for the base layer/enhancementlayer and the codeword index and a relation between the MCS for the baselayer/enhancement layer and the codeword index are broadcast to all UEslocated in a cell in a look up table manner. The codeword index may bepre-defined by being tied to the codeword for each user. Therefore, thebase station may estimate a code rate on the basis of a codeword indexwhen performing blind detection. By recognizing the base layer, the basestation may select a layer to be preferentially selected when performingSIC.

The use of the proposed scheme has an advantage in that hierarchicalcoding/modulation is utilized to decrease an error rate obtained througheach layer, to increase a total average system data rate that can betransmitted through each layer, or to support a greater number of userson average.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram illustrating a radio protocol architecture for auser plane.

FIG. 3 is a diagram illustrating a radio protocol architecture for acontrol plane.

FIG. 4 is a block diagram illustrating NOMA based downlinktransmission/reception (Tx/Rx) of a communication apparatus.

FIG. 5 is a block diagram illustrating NOMA based uplinktransmission/reception (Tx/Rx) of a communication apparatus.

FIG. 6 is a block diagram illustrating NCMA based downlinktransmission/reception (Tx/Rx) of a communication apparatus.

FIG. 7 is a block diagram illustrating NCMA based uplinktransmission/reception (Tx/Rx) of a communication apparatus.

FIG. 8 is a conceptual diagram illustrating a frequency axis of datatransmission according to UE-specific NCC.

FIG. 9 is a structural diagram illustrating basic transmission andreception of NCMA system.

FIG. 10 shows a contention-based random access procedure in an LTEsystem.

FIG. 11 shows a delay of control signaling and a delay of datatransmission according to an uplink processing procedure in an LTEsystem.

FIG. 12 shows an example of an asynchronous control operation through apre-defined implicit timing scheme.

FIG. 13 shows an example of a timing operation of a transceiver througha pre-defined implicit timing scheme.

FIG. 14 shows an example of a user grouping and resource zone allocationscheme for asynchronous control.

FIG. 15 shows an example of an uplink transmission scheme betweenmultiple UEs on the basis of a frequency spread resource configuration.

FIG. 16 is a flowchart showing a procedure of transmitting/receiving asignal for ULLS from a single user perspective.

FIG. 17 is a flowchart illustrating a procedure oftransmitting/receiving a signal for ULLS from a multi-user perspective.

FIG. 18 shows an example of a resource zone for performingcontention-based uplink connection and a resource zone for transmittingcontention-based uplink data according to an embodiment of the presentspecification.

FIG. 19 is a concept view showing an example of hierarchical modulation.

FIG. 20 is a block diagram showing an example of transmission/receptionfor a NOMA scheme to which hierarchical modulation is applied accordingto an embodiment of the present specification.

FIG. 21 is a flowchart showing a procedure of transmittingcontention-based data by applying hierarchical modulation according toan embodiment of the present specification.

FIG. 22 is a block diagram showing an apparatus for wirelesscommunication for implementing an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPPLTE uses the OFDMA in a downlink and uses the SC-FDMA in an uplink.

For clarity of explanation, the following description will focus on the3GPP LTE/LTE-A. However, technical features of the present invention arenot limited thereto.

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

A radio interface between the UE and the BS is called a Uu interface.Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram illustrating a radio protocol architecture for auser plane. FIG. 3 is a diagram illustrating a radio protocolarchitecture for a control plane. The user plane is a protocol stack foruser data transmission. The control plane is a protocol stack forcontrol signal transmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transmitted through a radio interface.

Between different PHY layers, i.e., a PHY layer of a transmitter and aPHY layer of a receiver, data are transferred through the physicalchannel. The physical channel is modulated using an orthogonal frequencydivision multiplexing (OFDM) scheme, and utilizes time and frequency asa radio resource.

A function of the MAC layer includes mapping between a logical channeland a transport channel and multiplexing/de-multiplexing on a transportblock provided to a physical channel over a transport channel of a MACservice data unit (SDU) belonging to the logical channel. The MAC layerprovides a service to a radio link control (RLC) layer through thelogical channel.

A function of the RLC layer includes RLC SDU concatenation,segmentation, and reassembly. To ensure a variety of quality of service(QoS) required by a radio bearer (RB), the RLC layer provides threeoperation modes, i.e., a transparent mode (TM), an unacknowledged mode(UM), and an acknowledged mode (AM). The AM RLC provides errorcorrection by using an automatic repeat request (ARQ).

Functions of a packet data convergence protocol (PDCP) layer in the userplane include user data delivery, header compression, and ciphering.Functions of a PDCP layer in the control plane include control-planedata delivery and ciphering/integrity protection.

A radio resource control (RRC) layer is defined only in the controlplane. The RRC layer serves to control the logical channel, thetransport channel, and the physical channel in association withconfiguration, reconfiguration and release of radio bearers (RBs).

An RB is a logical path provided by the first layer (i.e., the PHYlayer) and the second layer (i.e., the MAC layer, the RLC layer, and thePDCP layer) for data delivery between the UE and the network. Theconfiguration of the RB implies a process for specifying a radioprotocol layer and channel properties to provide a particular serviceand for determining respective detailed parameters and operations. TheRB can be classified into two types, i.e., a signaling RB (SRB) and adata RB (DRB). The SRB is used as a path for transmitting an RRC messagein the control plane. The DRB is used as a path for transmitting userdata in the user plane.

When an RRC connection is established between an RRC layer of the UE andan RRC layer of the network, the UE is in an RRC connected state, andotherwise the UE is in an RRC idle state.

Data is transmitted from the network to the UE through a downlinktransport channel Examples of the downlink transport channel include abroadcast channel (BCH) for transmitting system information and adownlink-shared channel (SCH) for transmitting user traffic or controlmessages. The user traffic of downlink multicast or broadcast servicesor the control messages can be transmitted on the downlink-SCH or anadditional downlink multicast channel (MCH). Data are transmitted fromthe UE to the network through an uplink transport channel Examples ofthe uplink transport channel include a random access channel (RACH) fortransmitting an initial control message and an uplink SCH fortransmitting user traffic or control messages.

Examples of logical channels belonging to a higher channel of thetransport channel and mapped onto the transport channels include abroadcast channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH), a multicasttraffic channel (MTCH), etc.

FIG. 4 is a block diagram illustrating NOMA based downlinktransmission/reception (Tx/Rx) of a communication apparatus.

In a Non-orthogonal Coded Multiple Access (NCMA) scheme for transmittingmulti-UE (or multi-user) information by allocating the multi-UEinformation to the same resource, a transmitter and receiver structurefor downlink support as shown in FIG. 4 is general. The NOMA system maybe referred to as Multiuser Superposition Transmission (MUST) in the3GPP standardization task. The NOMA system is considered as the elementtechnology of the next generation 5G system intended to obtaintransmission capacity gain or increase the number of simultaneousaccesses as compared with the LTE system by transmitting information fora plurality of UEs to the same time-frequency resource throughsuperposition. Examples of the NOMA based technology of the nextgeneration 5G system include MUST for identifying UEs based on a powerlevel, Sparse Code Multiple Access (SCMA) that uses sparse complexcodebook based modulation, and interleave division multiple access(IDMA) that uses a user-specific interleaver.

In case of the MUST system, the transmitter of FIG. 4 varies powerallocation of each symbol after modulation of multi-UE data or transmitsthe multi-UE data by hierarchically modulating the multi-UE data basedon hierarchical modulation, and the receiver demodulates the data of themulti-UE (hereinafter, referred to as multi-UE data) through multi-UEdetection (or multiuser detection) (MUD).

In case of the SCMA system, the transmitter of FIG. 4 replaces amodulation procedure of a forward error correction (FEC) encoder andmodulation procedure for multi-UE data with a sparse complex codebookmodulation scheme which is previously scheduled, and the receiverdemodulates the multi-UE data through MUD.

In case of the IDMA system, the transmitter of FIG. 4 modulates FECencoding information for multi-UE data through a UE-specificinterleaver, and the receiver demodulates the multi-UE data through MUD.

Each system may demodulate the multi-UE data in various MUD schemes.Examples of the various MUD schemes include Maximum Likelihood (ML),Maximum joint A posteriori Probability (MAP), Message Passing Algorithm(MPA), Matched Filtering (MF), Successive Interference Cancellation(SIC), Parallel Interference Cancellation (PIC), and CodewordInterference Cancellation (CWIC). There may be a difference indemodulation complexity and processing time delay in accordance witheach demodulation scheme or each demodulation attempt.

FIG. 5 is a block diagram illustrating NOMA based uplinktransmission/reception (Tx/Rx) of a communication apparatus.

A transmitter and receiver structure for uplink support of the NOMAbased system that transmits information of multi-UE (hereinafter,referred to as multi-UE information) by allocating the multi-UEinformation to the same resource is shown in FIG. 5. Each system maytransmit multi-UE data in the same manner as the description of thedownlink structure of FIG. 4 and modulate the multi-UE data through thereceiver. Since the NOMA based systems transmit multi-UE signals to thesame time-frequency resource through superposition, the systems have ahigher decoding error rate as compared with the LTE system but maysupport higher frequency usage efficiency or more massive connectivity.The NOMA systems may achieve higher frequency usage efficiency or moremassive connectivity while maintaining a decoding error through codingrate control in accordance with a system environment.

Since the NOMA based systems allocate data of multi-UEs to the sameresource, interference of multi-UE data is necessarily generated ascompared with allocation of single-UE data. A signal of the kth receiverin the NOMA based system of FIG. 4 is simply expressed as illustrated inthe following Equation 1.

$\begin{matrix}{y_{k} = {{{\sum\limits_{n = 1}^{K}{h_{k}s_{n}}} + n_{k}} = {{h_{k}s_{k}} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{h_{k}s_{n}}} + n_{k}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In this case, h_(k) means a channel from the transmitter to the kthreceiver, s_(k) means a data symbol to the kth receiver, and n_(k) meanssignal noise. K is the number of multiple UEs allocated to the sametime-frequency resource.

The second term

$\sum\limits_{{n \neq k},\;{n = 1}}^{K}{h_{k}s_{n}}$of the third formula of the Equation 1 indicates multiuser interference(MUI) signal according to a data symbol to another receiver. Therefore,transmission capacity according to the received signal is simplyexpressed as illustrated in the following Equation 2.

$\begin{matrix}{\mspace{79mu}{{C = {\sum\limits_{k = 1}^{K}R_{k}}}{{R_{k} = {{\log_{2}\left( {1 + \frac{{{h_{k}s_{k}}}^{2}}{{{\sum\limits_{{n \neq k},\;{n = 1}}^{K}{h_{k}s_{n}}}}^{2} + \sigma_{k}}} \right)} = {\log_{2}\left( {1 + \frac{{Channel}\mspace{14mu}{Gain}}{{MUI} + {Noise}}} \right)}}},\;{\forall k}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In transmission capacity of the above Equation 2, the number of Rk addedin accordance with increase of K may be increased, whereby increase of Cmay be expected. However, each Rk may be reduced due to increase of MUIin accordance with increase of K, entire transmission capacity C may bereduced. In accordance with the MUD scheme, even though data of each UEmay be demodulated while MUI is being effectively reduced, the presenceof MUI reduces entire transmission capacity and requires MUD of highcomplexity. If MUI occurrence of data transmission of the multi-UE isminimized, higher transmission capacity may be expected. Alternatively,if MUI occurrence for data transmission of the multi-UE may becontrolled quantitatively, higher transmission capacity may be plannedby scheduling of data superposition of the multi-UE. Therefore, thedevelopment of multi-UE access technology that may control MUI accordingto data superposition transmission of the multi-UE is required. Thedevelopment of multi-UE access technology that may control MUI generatedduring data superposition transmission of the multi-UE to the sametime-frequency resource is required.

Therefore, the present invention suggests a non-orthogonal codedmultiple access (NCMA) that minimizes multi-UE interference of the nextgeneration 5G system.

FIG. 6 is a block diagram illustrating NCMA based downlinktransmission/reception (Tx/Rx) of a communication apparatus, and FIG. 7is a block diagram illustrating NCMA based uplink transmission/reception(Tx/Rx) of a communication apparatus.

The present invention suggests an NCMA scheme that minimizes multi-UEinterference when data of multi-UE are transmitted to the sametime-frequency resource through superposition. FIGS. 6 and 7 illustratedownlink and uplink transmitter and receiver structures of the NCMAsystem that performs superposition transmission by using UE specificnon-orthogonal code cover (NCC) when multi-UE information is allocatedto the same time-frequency resource. The transmitter/receiver (ortransmitting side/receiving side) allocates UE-specific NCC to each UEby using a non-orthogonal codebook which is previously defined.

The codeword mentioned in the present invention means a complex elementvector selected by (or allocated to) each UE to perform non-orthogonalmultiple access. The codebook means a set of codewords used by each UEto perform non-orthogonal multiple access. The codebook mentioned asabove may exist as a plurality of codebooks. The UE-specific NCC meansthat the complex element vector of the codebook selected by (orallocated to) each UE is used for a symbol to be transmitted. Therefore,the NCC (or UE-specific NCC) may be expressed as codebook index andcodeword index. The non-orthogonal codebook is expressed as illustratedin the following Equation 3.

$\begin{matrix}{C = {\left\lbrack {c^{(1)}\mspace{14mu}\ldots\mspace{14mu} c^{(K)}} \right\rbrack = \begin{bmatrix}c_{1}^{(1)} & \ldots & c_{1}^{(K)} \\\vdots & \ddots & \vdots \\c_{N}^{(1)} & \ldots & c_{N}^{(K)}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In the above Equation 3, c^((j)) is a codeword for the jth UE, and acodeword set for a total of K UEs becomes a codebook C. Use of c^((j))for data transmission of the jth UE is defined as NCC. Also, thecodebook may be expressed as a vector length N of the codeword and thenumber K of codewords. In this case, N means a spreading factor, and Kmeans a superposition factor. For convenience of description, althoughone codeword is used for one UE, a plurality of codewords may be used byone UE or one codeword may be used by a plurality of UEs. Also, one ormore codewords allocated to one UE may be subjected to hopping ofcodewords by use of different codewords in the same codebook or use ofdifferent codewords in different codebooks in accordance with time orusage frequency.

UE-specific NCC may be allocated by connection with UE ID in RRCconnection process, or may be allocated through DCI (downlink controlinformation) format included in a downlink control channel (for example,PDCCH).

In case of an uplink environment used for contention based multipleaccess (MA), a UE may select non-orthogonal codewords randomly orthrough connection with UE ID. At this time, UE-specific NCC is notallocated by a base station but directly selected by a UE, whereby NCCcontention between multiple UEs may occur. A success rate foridentification of multi-UE information is reduced due to MUD if there iscontention of NCC in the base station which is a receiver.

The UE-specific NCC may be defined by Grassmannian line packing, and achordal distance formed by two random vectors in the same subspace isalways maintained equally. That is, the chordal distance may be obtainedmathematically or algorithmically as a codebook that satisfiesmin_(C)(max_(1≤k<j≤K)√{square root over (1−|c^((k)*)*c^((j))|²)}), C⊂

^(N×K).   The UE-specific NCC has features as expressed by the following Equation4.

$\begin{matrix}{\quad\left\{ \begin{matrix}{{{{c^{{(k)}^{*}} \cdot c^{(k)}}} = 1},\;{\forall k},{k = 1},\ldots\;,K,} \\{{{{if}\mspace{14mu} N} > K},{{{c^{{(k)}^{*}} \cdot c^{(j)}}} = \delta},{\forall k},{\forall j},{k = 1},\ldots\;,K,{j = 1},\ldots\;,K,} \\{{{{if}\mspace{14mu} N} \leq K},{{{c^{{(k)}^{*}} \cdot c^{(j)}}} = 0},{\forall k},\;{\forall j},{k = 1},\ldots\;,K,{j = 1},\ldots\;,{K.}}\end{matrix} \right.} & \left\lbrack {{Equ}\;{ation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In this case, c^((k)*) is a conjugate codeword of c(k). The features ofthe Equation 4 are as listed in the followings (1), (2), and (3).

(1) Multiplication of the same codewords in the transmitter and thereceiver is 1.

(2) The chordal distance between a codeword and another codeword in thesame codebook is equally maintained.

(3) If N≤K, a codeword is orthogonal to another codeword.

The codebook having the above features is previously scheduled by thetransmitter/receiver (or transmitting side/receiving side) to configureUE-specific NCC. In this case, a lower bound of a chordal distance

$\delta_{N,\; K} \geq \sqrt{1 - \frac{\left( {N - 1} \right)K}{N\left( {K - 1} \right)}}$according to two random codewords is obtained. Therefore, MUI forsuperposition transmission of multi-UE data is determined by beingminimized by the lower bound. Also, since the chordal distance for thetwo random codewords is always maintained equally, statisticalprediction of MUI may be performed by the number of UEs. If the numberof UEs is determined, since a decoding error rate of the receiver may bepredicted by MUI value, MCS level may be controlled based oninterference for multi-UE superimposition transmission. For example,when K codewords are transmitted in (N×1) dimension, if the receiverperforms decoding using its codewords, 1 is decoded from its codeword,and statistical interference of δ_(N,K)(K−1) remains from another K−1codewords. This value is varied depending on an optimization level of acodebook design. Also, since a difference in a value of δ_(N,K) existsdepending on the optimization level of the codebook design, the number Kof superposition UEs or the number N of used resources may be varieddepending on Required SINR or target QoS of the communication system,whereby the MUI value may be controlled.

The embodiment of the non-orthogonal codebook is expressed in the formof 3GPP TS 36.211 as listed in that following Tables 1 and 2, and may beused as UE-specific NCC.

Table 1 illustrates a codebook in case of Spreading Factor N=2.

TABLE 1 # of codewords (Max. # of users: K) Examples of spreadingcodebook [c⁽¹⁾ . . . c^((K))] 2 $\quad\begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}$ 3 $\quad\begin{bmatrix}{{- 0.5078} - {0.2451i}} & {{- 0.8055} + {0.5684i}} & {{- 0.1483} - {0.4194i}} \\{0.5640 - {0.6034i}} & {0.1640 + {0.0357i}} & {{- 0.8751} - {0.1904i}}\end{bmatrix}$ 4 $\quad\begin{bmatrix}{{- 0.4907} - {0.7256i}} & {{- 0.6440} - {0.5906i}} & {{- 0.1657} + {0.2160i}} & {{- 0.5775} - {0.2480i}} \\{0.4510 + {0.1709i}} & {{- 0.4452} + {0.1956i}} & {0.9349 - {0.2279i}} & {{- 0.3586} - {0.6902i}}\end{bmatrix}$

Table 2 illustrates a codebook in case of Spreading Factor N=4.

TABLE 2 # of codewords (Max. # of users: K) Examples of spreadingcodebook [c⁽¹⁾ . . . c^((K))] 4 $\quad\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}$ 6 $\quad\begin{bmatrix}\left\lbrack {{- 0.0557} - {0.4476i}} \right. & {{- 0.1684} - {0.8131i}} & {{- 0.0149} + {0.2255i}} & {\;\cdots} \\\; & {{- 0.0198} - {0.1206i}} & {{- 0.3294} - {0.3689i}} & {{- 0.0487} + {0.4148i}} \\{0.4023 - {0.1460i}} & {{- 0.4021} + {0.2118i}} & {{- 0.6703} + {0.0282i}} & {\;\cdots} \\\; & {{- 0.6521} - {0.4251i}} & {{- 0.0729} - {0.0903i}} & {{- 0.2158} - {0.3003i}} \\{0.1499\mspace{31mu} 0.3961i} & {0.0471\mspace{25mu} 0.2647i} & {0.3131\mspace{25mu} 0.5204i} & {\;\cdots} \\\; & {{- 0.5576} - {0.0206i}} & {0.6726 - {0.0552i}} & {0.0357 + {0.0924i}} \\{0.5675 + {0.3346i}} & {{- 0.0866} + {0.1557i}} & {{- 0.0287} + {0.3624i}} & {\;\cdots} \\\; & {{- 0.0286} + {0.2589i}} & {0.4567 - {0.2792i}} & {0.6985 + {0.4372i}}\end{bmatrix}$ 8 $\quad\begin{bmatrix}{{- 0.2381} - {0.8369i}} & {{- 0.6599} - {0.1222i}} & {{- 0.6557} - {0.1776i}} & {{- 0.1561} + {0.0861i}} & \cdots \\\; & {{- 0.1374} + {0.1275i}} & {{- 0.1849} + {0.3859i}} & {{- 0.2426} - {0.2248i}} & {{- 0.1703} - {0.0604i}} \\{{- 0.2593} - {0.3320i}} & {0.4906 + {0.0221i}} & {0.3934 + {0.2749i}} & {{- 0.3453} - {0.2068i}} & \cdots \\\; & {{- 0.5596} + {0.0272i}} & {0.0616 - {0.0315i}} & {{- 0.3027} - {0.3133i}} & {{- 0.7664} + {0.1256i}} \\{{- 0.1249} + {0.0320i}} & {0.0425 + {0.3856i}} & {0.0440 - {0.3295i}} & {{- 0.3979} + {0.0525i}} & \cdots \\\; & {{- 0.5272} - {0.2195i}} & {0.0649 - {0.8770i}} & {{- 0.2452} + {0.4427i}} & {{- 0.0149} - {0.4727i}} \\{{- 0.2180} - {0.0342i}} & {0.3968 - {0.0250i}} & {{- 0.3444} - {0.2811i}} & {{- 0.7817} - {0.1845i}} & \cdots \\\; & {0.2417 + {0.5162i}} & {0.1956 - {0.0203i}} & {0.4625 - {0.4805i}} & {0.0794 - {0.3663i}}\end{bmatrix}$

Various values may be obtained using mathematical equation or algorithmin addition to the above Tables 1 and 2.

FIG. 8 is a conceptual diagram illustrating a frequency axis of datatransmission according to UE-specific NCC.

FIG. 8 illustrates a concept that a transmitter (or transmitting side)transmits kth UE data on a frequency axis through UE-specific NCC. WhenUE-specific NCC defined by Grassmaniann line packing is previouslyscheduled by the transmitter and the receiver, data for the kth UE ismultiplied by a codeword corresponding to the kth UE. At this time, onedata symbol sk corresponds to a codeword vector c^((k)) of (N×1)dimension. Then, N elements of the codeword correspond to N subcarriers.

That is, in FIG. 8, since one data symbol is transmitted to Nsubcarriers, the same time-frequency resource efficiency is reduced to1/N as compared with the legacy LTE system. On the other hand, if N ormore symbols are transmitted by superposition, time-frequency resourceefficiency is increased as compared with the LTE system. For example, ifK symbols are transmitted by superposition in case of N<K, frequencyresource efficiency is increased as much as K/N times.

FIG. 9 is a structural diagram illustrating basic transmission andreception of NCMA system.

FIG. 9 is a basic transmission and reception structural view of NCMAsystem that uses UE-specific NCC. Data symbols for each UE are convertedto UE-specific NCC corresponding to each UE and superposed in thetransmitter. A frequency axis signal of a superposed N length isconverted to a time-axis signal through N-IFFT, whereby OFDMtransmission is performed, and the receiver restores the time-axissignal to a frequency-axis signal through N-FFT. The restoredfrequency-axis signal decodes each UE data symbol using a conjugatecodeword of UE-specific NCC corresponding to each UE. The decoded s_(k)may include MUI depending on the number of superposed UEs, and exacts_(k) decoding is available through MUD. At this time, the length of thefrequency-axis signal converted in accordance with UE-specific NCC whichis previously defined may be shorter than N. For example, if twofrequency-axis signal vectors converted to UE-specific NCC of N/2 lengthare connected in series to form N length, it will be apparent thatdemodulation is available in the receiver even in case of N-FFT.

In case of downlink, a detection equation for data decoding in the kthUE receiver is expressed as illustrated in the following Equation 5.

$\begin{matrix}{{y_{k} = {{\sum\limits_{n = 1}^{K}{H_{k}c^{(n)}s_{n}}} + n_{k}}},} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{\hat{y}}_{k} = {\left\lbrack \frac{\left\lbrack y_{k} \right\rbrack_{j}}{\left\lbrack H_{k} \right\rbrack_{j,j}} \right\rbrack_{{j = 1},\;\ldots\;,\; N} = {{\sum\limits_{n = 1}^{K}{c^{(n)}s_{n}}} + {\hat{n}}_{k,}}}} & \;\end{matrix}$

In the above Equation 5, H_(k) means (N×N) channel matrix from the kthtransmitter to the receiver, and includes frequency-axis channelcoefficients as a diagonal matrix. c^((k)) is (N×1) UE-specific NCCvector for the receiver at the kth transmitter, s_(k) is a data symbolto the kth receiver, and n means (N×1) signal noise vector. K is thenumber of multi-UEs allocated to the same time-frequency resource. Inthis case,

$\left\lbrack \frac{\lbrack A\rbrack_{j}}{\lbrack B\rbrack_{j,j}} \right\rbrack_{{j = 1},\;\ldots\;,\; N}$means division of the jth element of vector A and the jth diagonalelement of matrix B. If the vector A is a diagonal matrix, the vector Ameans element division of diagonal matrixes.

A signal of desired codewords and noise remain through channelcompensation in the above Equation 5, and are detected as expressed bythe following Equation 6 through conjugate codeword of UE-specific NCCof the receiver.

$\begin{matrix}\begin{matrix}{{{\overset{\sim}{y}}_{k} = {{c^{{(k)}^{*}} \cdot {\hat{y}}_{k}} = {{{c^{{(k)}^{*}} \cdot c^{(k)}}s_{k}} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{{c^{{(k)}^{*}} \cdot c^{(n)}}s_{n}}} + {\overset{\sim}{n}}_{k}}}},} \\{= {s_{k} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{c^{{(k)}^{*}\; \cdot \; c^{(n)}}s_{n}}} + {{\overset{\sim}{n}}_{k}.}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In the above Equation 6, the second item of the last column indicatesMUI, and may be removed or reduced through the MUD scheme.

In case of uplink, a detection equation for data decoding in thereceiver of the base station is expressed as illustrated in thefollowing Equation 7.

$\begin{matrix}{{y = {{{\sum\limits_{n = 1}^{K}{H_{n}c^{(n)}s_{n}}} + n} = {{H_{k}c^{(k)}s_{k}} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{H_{n}c^{(n)}s_{n}}} + n}}},} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The second term of the third formula of the Equation 7 indicatesmulti-UE interference signal MUI according to a data symbol to anotherreceiver. A detection equation of the receiver for data decoding of thekth UE is expressed as illustrated in the following Equation 8.

$\begin{matrix}{{{\hat{y}}_{k} = {\left\lbrack \frac{\lbrack y\rbrack_{j}}{\left\lbrack H_{k} \right\rbrack_{j,\; j}} \right\rbrack_{{j = 1},\;{\ldots\mspace{14mu} N}} = {{c^{(k)}s_{k}} + {\sum\limits_{n = 1}^{K}{\left\lbrack \frac{\left\lbrack H_{n} \right\rbrack_{j,\; j}}{\left\lbrack H_{k} \right\rbrack_{j,\; j}} \right\rbrack_{{j = 1},\;{\ldots\mspace{14mu} N}}c^{(n)}s_{n}}} + \hat{n}}}},} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

A signal of desired codewords, MUI, and noise remain through channelcompensation for the kth UE data, and are detected as expressed by thefollowing Equation 9 through conjugate codeword of UE-specific NCC ofthe receiver.

$\begin{matrix}\begin{matrix}{{\hat{y}}_{k} = {c^{{(k)}^{*}} \cdot {\hat{y}}_{k}}} \\{{= {{{c^{{(k)}^{*}} \cdot c^{(k)}}s_{k}} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{{c^{{(k)}^{*}} \cdot \left\lbrack \frac{\left\lbrack H_{n} \right\rbrack_{j,\; j}}{\left\lbrack H_{k} \right\rbrack_{j,\; j}} \right\rbrack_{{j = 1},\;\ldots\;,\; N}}c^{(n)}s_{n}}} + \overset{\sim}{n}}},} \\{= {s_{k} + {\sum\limits_{{n \neq k},\;{n = 1}}^{K}{{c^{{(k)}^{*}} \cdot \left\lbrack \frac{\left\lbrack H_{n} \right\rbrack_{j,\; j}}{\left\lbrack H_{k} \right\rbrack_{j,\; j}} \right\rbrack_{{j = 1},\;\ldots\;,\; N}}{c^{(n)} \cdot s_{n}}}} + {\overset{\sim}{n}.}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

In the above Equation 9, the second item of the last column indicatesMUI, and may be removed or reduced through the MUD scheme. At this time,frequency-axis channel change of

$\left\lbrack \frac{\left\lbrack H_{n} \right\rbrack_{j,\; j}}{\left\lbrack H_{k} \right\rbrack_{j,\; j}} \right\rbrack_{{j = 1},\;\ldots\;,\; N}$causes a change of MUI value when MUD according to UE-specific NCC isperformed due to a change of a channel environment from the multi-UE.For convenience of description, a single transmitting and receivingantennas is provided, it will be apparent that the same scheme isapplied to even an environment where multiple antennas are used.

According to the description related to the aforementioned NCMA scheme,it is possible to achieve higher frequency usage efficiency or moremassive connectivity in accordance with the number of superposed UEswhile controlling MUI according to multi-UE data superpositiontransmission.

The present specification proposes a contention-based multiple access(MA) scheme. The proposed scheme includes an operating scheme based onhierarchical coding and modulation in the contention-based MA.Hereinafter, the contention-based MA scheme will be described.

FIG. 10 shows a contention-based random access procedure in an LTEsystem.

In a wireless communication system, the contention-based MA scheme shownin FIG. 10 is a typical technique. An uplink access scheme in an LTEcommunication system is shown in FIG. 10. In addition, the access schememay be used in an ad-hoc network such as device to device (D2D) orvehicular to everything (V2X) and a cellular-based scheme such asLTE-advanced (LTE-A) or machine type communication (MTC).

The contention-based MA scheme starts when a scheduling request (SR) isperformed from a UE to an eNB (S1010), and scheduling information of theeNB is received (S1020). Scheduling information received from the eNBincludes timing adjustment or timing advance (TA) for synchronizationbetween signals received from multiple users, a cell, ID, and a grant(e.g., it is transmitted through a PDCCH as control informationincluding MCS level information or resource allocation information) foruplink access. In general, a communication system is a communicationsystem in which limited radio resources are used by multiple UEs.However, since one UE cannot know a state of another UE, there may be acase where the multiple UEs request for resource allocation with respectto the same resource. Accordingly, the eNB resolves collision ofresources requested by the multiple UEs in one contention, and transmitsinformation thereof (S1040). In addition, the eNB and the UE transmituplink data by exchanging control information for network access andHARQ (S1030).

FIG. 11 shows a delay of control signaling and a delay of datatransmission according to an uplink processing procedure in an LTEsystem.

V2X, emergency service, machine control, or the like targeting anultra-low latency service (ULLS) is considered in a next-generationwireless communication system. The ULLS has a very limited end-to-end(E2E) latency requirement and requires a high data rate. For example,E2E Latency<1 ms, DL Data Rate: 50 Mbps, UL Data Rate: 25 Mbps. Ingeneral, the E2E latency is determined by a network delay, a processingdelay, and an air interface delay. The legacy contention-based multipleaccess scheme essentially requires heavy controlling as shown in FIG. 4,and thus has a long air interface delay. A delay of control signalingand a delay of data transmission are shown in FIG. 11 according to anuplink processing procedure of the legacy LTE system. Therefore, thereis a need for a scheme capable of simplifying a control procedure forULLS and effectively resolving contention, and a multiple access schemecapable of increasing a data transfer rate.

Accordingly, a scheme capable of simplifying a control procedure andresolving contention and a multiple access scheme and resourceallocation scheme capable of increasing a data transfer rate areproposed for a low latency service of the next-generation wirelesscommunication system.

In order to achieve the ULLS, a multiple access control scheme isproposed in which a control signaling procedure for multiple access issimplified and immediate data transmission of a UE is ensured.

In particular, in order to ensure the service, it is necessary toachieve: 1) a decrease in initial control signaling (timing advance (TA)and grant reception or the like) for UL transmission; and 2) a decreasein reception time of ACK/NACK for data transmission. A technique forenabling asynchronous control for multi-user transmission occurring whenTA is not performed and uplink transmission without reception of an SRand a grant is proposed to achieve the condition 1). In addition, atechnique for minimizing a traffic transfer completion time point of theUE is proposed to achieve the condition 2).

Method 1: Asynchronous Multiple Access Based on Control SignalingReduction for Ultra-Low Latency

In order to achieve the condition 1), it is assumed that each UEperforms data transmission immediately without performing TA andscheduling from an eNB upon traffic generation based on datatransmission. From a receiving eNB perspective, there may be a problemin that data reception of multiple users is not synchronized and aproblem in that collision occurs between data of multiple users. Even ifa multiple access scheme (e.g., Interleave Division Multiple Access(IDMA) or Sparse Code Multiple Access (SCMA), Power Level Non-OrthogonalMultiple Access (NOMA)) robust to an asynchronous property and datacollision of multiple users is used, asynchronous data between multipleusers at a receiver may make it difficult to distinguish between usersand may be a cause of reducing a data decoding rate. Accordingly, thereis a need for a multiple access scheme for asynchronous control.

The method 1 proposes a scheme of resolving an asynchronous problembetween multiple users, which occurs due to a decrease in controlsignaling for supporting ULLS. When performing uplink transmission, UEsresolve the asynchronous problem, which occurs when initial controlsignaling is not performed, through pre-defined implicit timing. Whentraffic is generated based on uplink data transmission, the UEs provideasynchronous control by performing symbol-based synchronization from atransmission perspective through pre-defined periodic timing. Inaddition, a timing offset from a reception perspective is controlled tobe within a cyclic prefix (CP) by performing user-grouping on UEs havinga similar propagation delay time and by allocating the same resourcezone. The user grouping is performed by an eNB according to apre-defined timing distance, and the resource zone is allocated inadvance to each user group. In this case, uplink data collision ofsynchronized UEs is identified through multi-user detection (MUD).

When the proposed method is used, synchronized uplink data can betransmitted without a TA and a grant, and uplink data collisionoccurring in this case can be identified through MUD.

For example, a pre-defined implicit timing scheme for asynchronouscontrol is proposed. This may correspond to a method of removing atiming offset from a transmission perspective.

FIG. 12 shows an example of an asynchronous control operation through apre-defined implicit timing scheme.

Referring to FIG. 12, it is assumed that an eNB and each UE (i.e., UE 1,UE 2, and UE 3) share pre-defined timing Pre-defined implicit timing isdefined as a symbol unit, and a period thereof may differ depending on asymbol duration of a system environment. In this case, the pre-definedimplicit timing indicates periodicity, and a period thereof may bedefined variously such as a symbol, a sub-frame, a frame, or the like. AUE which requires immediate data transmission transmits informationregarding pre-defined implicit timing which is closest from a time pointthereof. Herein, the pre-defined implicit timing may be agreed fromdownlink synchronization, or may be agreed as absolute time in advancethrough pre-defined control information between the eNB and all UEs.However, the pre-defined implicit timing may be defined asT_(Implicit)(N)=T+T_(symbol)*N on the basis of an absolute timereference T. Herein, N=0, . . . , ∞. T_(symbol) may be a symbol length,sub-frame length, or frame length including a CP length.

For example, as shown in FIG. 12, when traffic of the UE 1 and the UE 2is generated between T_(Implicit)(k) and T_(Implicit)(k+1), uplinktransmission starts at the closest pre-defined implicit timingT_(Implicit)(k+1). Likewise, in case of the UE 3, when traffic isgenerated between T_(Implicit)(k+1) and T_(Implicit)(k+2), uplinktransmission starts at the closest pre-defined implicit timingT_(Implicit)(k+2).

FIG. 13 shows an example of a timing operation of a transceiver througha pre-defined implicit timing scheme.

Since the pre-defined implicit timing maintains synchronization on asymbol basis, UEs 1, 2, and 3 may ensure symbol synchronization from atransmission perspective even if uplink traffic is generated atdifferent time points as shown in FIG. 13. In this case, each UE maygenerate an uplink transmission latency of up to T_(symbol)(=71.4 us).

In this case, even if the transmission time point is maintained equallyas shown in FIG. 13, a receiving eNB performs reception at a differenttiming according to a physical distance and a multi-path channelexperienced by each UE. Therefore, the receiving eNB experiences atiming variance Δt of each UE. Accordingly, there is a need for a methodfor controlling Δt within a CP duration.

For another example, a user grouping and resource zone allocation schemefor asynchronous control is proposed. This may correspond to a method ofcontrolling a timing offset within a CP from a reception perspective.

FIG. 14 shows an example of a user grouping and resource zone allocationscheme for asynchronous control.

Referring to FIG. 14, an eNB receives information regarding a timingdistance of a UE periodically or upon downlink transmission or uplinktransmission of the UE. Herein, the timing distance is determined by notonly a physical distance but also a system environment or a propagationdelay caused by a multi-path of the UE. As shown in the left side ofFIG. 14, the eNB may configure a fractional timing distance zone andperform user grouping by considering the timing distance betweenmultiple users.

For example, if Δt is controlled with a CP duration, user grouping isperformed by assuming that UEs of which a propagation delay time causedby a physical distance or a multi-path corresponds to 0−Δt are in atiming distance zone A. In a similar manner, user grouping is performedby assuming that UEs of which a propagation delay time corresponds toΔt−2*Δt are in a timing distance zone B. Therefore, one user group has atiming offset within a CP duration from a receiving eNB perspective.Herein, the timing variable Δt may be defined variously depending on asystem environment (e.g., a cell radius or a CP duration or the like).In this case, as a magnitude of Δt decreases, a timing offset from areception perspective decreases, whereas a timing distance zone issubdivided and the number of user group increases, which leads to anincrease in complexity of a system operation. On the other hand, as themagnitude of Δt increases, a timing offset from a reception perspectiveincreases, whereas simplicity of the timing distance zone and the numberof user groups decrease, which leads to a decrease in complexity of thesystem operation. In addition, when Δt is set beyond CP, the receivingeNB may identify a signal through a rake receiver, and may detect asignal through inverse Fourier transform (IFT) for each individualsignal. The user grouping is achieved periodically or upon downlinktransmission or uplink transmission of the UE irrespective of immediateuplink data transmission of the UE.

For example, in the left side of FIG. 14, the eNB divides a timingdistance zone into four steps A, B, C, and D through informationregarding a timing distance of UEs, and allocates the UEs 1, 2, and 3having similar timing distances to the timing distance zone A. Herein, ascheme of dividing the timing distance zone may control Δt of FIG. 14within a CP duration. A condition of controlling Δt may vary dependingon various carrier spacing and CP configurations. Therefore, when theeNB allocates the same resource zone to UEs allocated to the same timingdistance zone, each UE may perform immediate uplink transmission byconsidering only pre-defined implicit timing irrespective of timing ofanother user or UL grant/time advance from the eNB. Even if timing of aresource block differs in immediate uplink transmission of each UE,symbol timing within a CP duration may be ensured.

In FIG. 14, the pre-defined resource zone may vary depending on a systemenvironment or the number of users to be connected to the eNB. Forexample, in FIG. 14, a pre-defined resource zone may be configuredaccording to a fractional timing distance zone, and the pre-definedresource zone may be divided in a time division, frequency division, andtime-frequency division manner. Herein, in case of time division, it maybe divided variously such as a symbol, a slot, a sub-frame, a frame, orthe like, or division may not be achieved. Similarly, in case offrequency division, it may be divided variously such as a sub-carrier, asub-band, a total-band, or the like, or division may not be achieved.Herein, when it is said that division is not achieved, this means thatthe entire resources can be used.

In FIG. 14, the UEs 1, 2, and 3 of the same timing distance zone A sharethe entirety of the same resource zone by performing uplink transmissionto the resource zone A. Therefore, since UEs performing uplinktransmission in the same resource zone perform uplink transmission withthe same resource, a receiving eNB must identify data of the UEs. Amultiple access technique capable of multi-user detection (MUD) may beutilized to identify multi-user data. For example, IDMA, SCMA, PowerLevel NOMA, or the like may be utilized.

Method 2: Time-Frequency Resource Sharing Based on Asynchronous MultipleAccess for Ultra-Low Latency

In order to achieve the condition 2), each UE must minimize a latencyfrom a UL traffic generation time point to a traffic transmissioncompletion time point. In order to minimize the latency, each UE needsto start data transmission simultaneously with UL traffic generationthrough as many resources as possible. Accordingly, there is a need fora scheme of performing immediate data transmission without a loss of adecoding rate while multiple users share limited resources.

The present specification proposes a scheme of minimizing immediate datatransmission start and traffic transmission completion time points in amulti-user access scheme of sharing limited resources. UEs havingdifferent UL transmission requests and traffic sizes perform ULtransmission through a multiple access scheme in which MUD is possible,by considering only pre-defined implicit timing mentioned in themethod 1. Since users in the resource zone of the method 1 have a timingoffset within a CP, UL transmission is performed without consideringother users' timing or resource occupation. Then, a receiving eNBperforms MUD at a symbol level. The MUD scheme may vary depending on themultiple access scheme, and signals of multiple users are identifiedthrough successive interference cancelation (SIC) or parallelinterference cancelation (PIC) or the like as an iterative decodingscheme. In addition, a latency from an air interface perspectivedecreases through a variable configuration of a limited resource zone.

When the proposed method is used, immediate data transmission can beperformed without a loss of a decoding rate while multiple users sharelimited resources.

For example, a UL transmission scheme between multiple UEs on the basisof a frequency spread resource configuration is proposed.

FIG. 15 shows an example of an uplink transmission scheme betweenmultiple UEs on the basis of a frequency spread resource configuration.

A UL transmission scheme of multiple UEs for minimizing a traffictransmission completion time point is exemplified in FIG. 15 on thebasis of a frequency spread resource configuration. UEs having differentUL transmission requests and traffic sizes perform UL transmissionthrough a multiple access scheme in which MUD is possible, byconsidering only the aforementioned pre-defined implicit timing. Forexample, when a UE A in which a UL transmission request first occursperforms transmission, a UE C performs UL transmission to the sameresource zone. In the same manner, when its transmission request occurs,each UE performs UL transmission without considering other users' timingor resource occupation. Then, a receiving eNB performs MUD at a symbollevel. The MUD scheme may vary depending on the multiple access scheme,and signals of multiple users may be identified through successiveinterference cancelation (SIC) or parallel interference cancelation(PIC) or the like as an iterative decoding scheme.

In the multiple access scheme of the method 2, a resource can beutilized variably since multiple UEs perform UL transmission by sharingthe same resource zone. In order to achieve a low latency from an airinterface perspective as shown in FIG. 15, an RB or a sub-band may beconfigured with a smaller transmission time interval (TTI) and a widersub-carrier or bandwidth. For example, a sub-carrier spacing 15 kHz of alegacy LTE system may be extended, and thus there may be a change in asymbol duration through various sub-carrier configurations such as 30KHz, 60 KHz, or the like, and even if there is a change in thesub-carrier spacing, it is apparent that the multiple access schemeproposed in the method 2 can be utilized. Likewise, even if various RBunits are configured such as 10 RB units, 14 RB units, or the like in 12sub-carriers, it is apparent that the aforementioned multiple accessscheme can be utilized. In a similar manner, the sub-band may also beconfigured variably.

For example, in FIG. 15, if traffic of the UE A is generated at a timet_(A) with a traffic amount which can be transmitted during a unit timeT_(A), when scheduling is performed through SC-FDMA or the like of thelegacy LTE, a transmission completion time may be expressed such ast_(ACK)=t_(A)+t_(control)+T_(A)/N_(carrier)/N_(symbol). Herein,t_(control) is a scheduling control time of TA and grant reception orthe like. N_(carrier) and N_(symbol) are frequency and time resourcesthat can be used by the UE A. On the other hand, if the conditions 1)and 2) are achieved according to the multiple access scheme proposed inthe methods 1 and 2, the transmission completion time may be expressedsuch ast_(ACK)=t_(A)+t_(Implicit)+T_(A)/(N_(carrier)*N_(user))/N_(symbol).Accordingly, although a traffic generation time t_(A) is identical, asshown in FIG. 13, it is apparent that t_(Implicit)<<t_(control).According to the legacy LTE, a maximum value of t_(Implicit) is 71.4 us,and t_(control) is 4-8 ms. In addition, since the UE A can occupy alltime frequency resources in the resource zone, the transmission timeT_(A) may be decreased in proportion to the number of occupying UEs. Incase of FIG. 15, since the number of occupying UEs is 4, a transmissiontime can be decreased to T_(A)/4. The aforementioned example may varydepending on variable utilization of resources, and there may be adifference in the time decrease according to a parameter change of achannel coding scheme considering a decoding rate decrease caused bymultiple access.

In the proposed frequency spread resource scheme, if the number of UEswhich perform simultaneous transmission increases, a decoding ratedecreases due to a decrease in MUD performance, and a retransmissionrequest may be performed. Therefore, a level of frequency spreadresource needs to be changed adaptively according to the number of UEsto be simultaneously connected. For example, if a maximum value ofsimultaneous transmission of the multi-user superposition access schemein use is 4, when simultaneous transmission is performed by four users,a current resource zone is bisected in a frequency domain to enablesimultaneous transmission of up to 8 users. The frequency divisioninformation is broadcast with an indication bit, and is informed to UEswhich use the current resource zone. The UEs continuously perform ULtransmission on the basis of the received indication bit.

Method 3: Asynchronous Multiple Access Based Signal Flow for Ultra-LowLatency

A signal flow from a transceiver perspective is required in order toperform the methods 1 and 2.

The present method proposes a signal flow from a transceiver perspectivefor performing the multi-user access scheme proposed in the methods 1and 2. A candidate group of a resource zone to be used in ULtransmission and control information for multi-user data transmissionare previously allocated to each UE by an eNB belonging thereto throughpre-defined control information. Each UE transmits an essential controlmessage to the eNB upon generation of UL traffic, and immediatelyperforms data transmission irrespective of UL transmission of anotheruser without any control from the eNB. Upon receiving controlinformation of the eNB without completion of data transmission, data maybe transmitted by changing a data transmission scheme according to thereceived control information.

When the proposed method is used, immediate data transmission ispossible without having to wait for control information reception of theeNB upon generation of UL data traffic of the UE.

For example, a signal flow for ULLS is proposed from a single userperspective.

FIG. 16 is a flowchart showing a procedure of transmitting/receiving asignal for ULLS from a single user perspective.

Conditions 1) and 2) for ULLS can be achieved by the methods 1 and 2,and the uplink procedure of FIG. 11 may change as shown in FIG. 16.

In a structure of FIG. 16, a control signaling procedure of the legacymultiple access scheme is simplified, and immediate data transmission ofa UE is performed. It is assumed that a candidate group of a resourcezone to be used in UL transmission and control information formulti-user data transmission are allocated in advance to each UE by aneNB belonging thereto (S1610). Herein, the resource zone may beallocated based on a timing distance zone as shown in FIG. 14. Accordingto a system environment, a resource allocated for UL transmission may beconfigured in a divided manner, or may be configured as one zone withoutbeing divided. When one time-frequency resource is used by multipleusers, control information for multi-user data transmission is essentialcontrol information of a multiple access scheme for identifying this.For example, there may be a user-specific interleaver scheme or index ofIDMA, or a codebook scheme or codeword index of SCMA, a power controlscheme or power level of power level NOMA, or the like. Herein, aslong-term control information, pre-defined control information or thelike of FIG. 12 may be irrelevant to generation of UL informationtransmission traffic.

Upon generation of traffic of data transmission, each UE transmits onlyessential control information for network access (S1620), and transmitsdata immediately without grant reception or timing advance (S1630). Asshown in FIG. 16, L2/L3 messages for network access, a modulation andcoding scheme (MCS) level previously used, resource map informationcurrently being used, or the like may be included as the essentialcontrol information. Transmission of the essential control informationis a small amount of information which may affect a decoding rate ofsubsequent data transmission, and may need to be transmitted byconsidering repetition or a fixed MCS level capable of ensuring a highdecoding rate. In this case, an MCS level or power control of each useris determined autonomously by the UE on the basis of CQI information ina long-term perspective. For example, each user may perform the MCSlevel and power control on the basis of PDCCH information or DL RSSIinformation of a previous time. Alternatively, data may be transmittedwith a relatively lower level than an MCS level for UL transmission of aprevious time and with a higher level than a power level for ULtransmission of the previous time, thereby increasing receptionreliability.

Regarding an initially determined MCS level and power level, afterimmediate data transmission, MCS/power level adjustment andsynchronization may be performed based on timing advance and a shortgrant received through a PDCCH during a persistent data transmissiontime. For example, in FIG. 16, each UE transmits essential controlinformation without scheduling between multiple users upon generation ofdata transmission traffic (S1620). In addition, data is continuouslytransmitted without any control of the eNB (S1630). Upon receiving theessential control information, the eNB transmits MCS/power level controlinformation and timing advance information to each UE on the basis of acurrent UL resource state and timing information (S1640). Each UE whichhas continuously transmitted data without any control changes anMCS/power level from a time point of receiving control information ofthe eNB, and continuously transmits data by performing timing advance(S1650). In this case, an indication bit of frequency division may bereceived for the resource zone of the method 2. Control informationtransmission/reception of the eNB may be a selective method.

For another example, a signal flow for ULLS is proposed from amulti-user perspective.

FIG. 17 is a flowchart illustrating a procedure oftransmitting/receiving a signal for ULLS from a multi-user perspective.

Signaling for ULLS based on the multiple access scheme proposed in themethod 3 is exemplified in FIG. 17. In a multi-user case, it is apparentthat the conditions 1) and 2) can be achieved through the scheme of themethod 3, and data transmission can be performed immediately after ULtraffic is generated to be robust to an asynchronous property. An eNBpersistently decodes data of UEs corresponding to a resource zone, andupon recognizing decoding success or data reception, may performadditional control signaling for maintaining connection with the UE.

Hereinafter, a method of designing a contention zone forcontention-based multiple access is described.

A sequence, codeword, or the like described in the present specificationrefers to a frequency or time-axis complex vector used to classifymultiple users in NOMA. The complex vector may have orthogonal ornon-orthogonal properties depending on a configuration. In addition, thecomplex vector may be represented by a single scalar value according tothe configuration of the complex vector. In this case, it may be matchedwith the existing single resource single information transmission.Spreading mentioned in the present specification refers to frequency ortime-axis spreading, and the complex vector is used in the spreading. Inaddition, according to the configuration of the complex vector and aresource allocation scheme, transmission may be achieved withsuperposition in the same resource region or single transmission may beachieved without superposition.

FIG. 18 shows an example of a resource zone for performingcontention-based uplink connection and a resource zone for transmittingcontention-based uplink data according to an embodiment of the presentspecification.

It is assumed in the present specification that a contention zone 1830for contention-based UL connection or UL data transmission is broadcastto UEs on the basis of NOMA. For example, the UE performs downlinksynchronization through a DL synchronization signal (e.g., PSS and SSSof LTE, a DL synchronization signal proposed in new RAT, or the like).The UE receives system information (system information (SI) 1810, forexample, MIB information through PBCH of LTE, SIB in formation throughPDSCH, or to-be-broadcast system information proposed in new RAT) on thebasis of downlink synchronization. The synchronization signal and the SI1810 may be broadcast through a common control zone 1820, and all UEsmay decode the synchronization signal and the SI 1810.

Through the SI, the UE may recognize a resource region for performingcontention-based UL connection and a resource region for performingcontention-based UL data transmission. For example, through the SI 1810,a resource index corresponding to the common control zone 1820 may beindicated, or it may be agreed to use a fixed resource in advance. Inthis case, RNTI (e.g., RNTI for an identification of a contention zone)for decoding the common control zone 1820 may be newly defined, and thisis agreed in advance. Through the control information transmitted to thecommon control zone 1820, a resource index corresponding to thecontention zone 1830 may be indicated, or it may be agreed in advance touse a fixed resource. The method may enable transmission also in case ofa UE which is not in a connected state, that is, a UE in an idle state.Of course, information on the common control zone may be informed to UEsin the connected state through RRC instead of system information.

In FIG. 18, an x-axis direction is exemplified as a time domain, and ay-axis direction is exemplified as a frequency domain.

A contention zone type may be classified into: 1) a random access zonefor UL connection (e.g., a PRACH zone of LTE or a xPRACH zone of newRAT); 2) a scheduling request zone for allocating a UL data transmissionregion (an SR zone of LTE or an xSR zone of new RAT); 3) a UL controlzone for UL control transmission (a PUCCH zone of LTE, or an xPUCCH zoneof new RAT); and 4) a UL data zone for UL data transmission (a PUSCHzone of LTE or an xPUSCH zone of new RAT). Herein, it is assumed in thefollowing description that the contention zone is usually used for thecase 4).

Hereinafter, a method of operating a contention-based multiple accessscheme on the basis of hierarchical coding and modulation is described.

FIG. 19 is a concept view showing an example of hierarchical modulation.

Referring to FIG. 19, hierarchical modulation (HM) will be brieflydescribed.

The HM may be referred to or expressed as layered modulation.

The HM is one of techniques for multiplexing and modulating a pluralityof data streams into one symbol stream. Herein, base layer sub-symbolsand enhancement layer sub-symbols are synchronized together andsuperimposed before being transmitted.

When the HM is applied, a user (or user terminal) having an enhancedreceiver and good reception quality may demodulate and decode at leastone data stream.

A user terminal having a legacy receiver or poor reception quality maydemodulate and decode only a data stream transmitted in a base layerhaving a low coding rate and/or a low modulation order.

From an information-theory perspective, the HM is treated as onepractical implementation in superposition precoding, and is proposed toachieve a maximum sum rate of a Gaussian broadcast channel havingsuccessful interference cancellation at a receiving end (or receiver).

From a network operation perspective, when the HM is applied, a networkoperator may persistently target user terminals having differentservices or QoS.

However, due to inter-layer interference (ILI), the conventional HMexperiences a decrease in a ratio that can be achieved by a base layerdata stream because of interference from high layer signal(s).

For example, for two-layer symbols subjected to the HM and including a16QAM base layer and a QPSK enhancement layer, a throughput loss causedby the ILI in the base layer may increase up to about 1.5 bits/symbolwhen a total reception signal-to-noise ratio (SNR) is about 23 dB. Thismeans that a loss of a throughput that can be achieved at the 23 dB SNRin the base layer is about 37.5%(1.5/4). On the other hand, ademodulation error rate of any one of base layer and enhancement layersymbols also increases.

FIG. 20 is a block diagram showing an example of transmission/receptionfor a NOMA scheme to which HM is applied according to an embodiment ofthe present specification.

The present specification describes a scheme in which multi-userinformation is transmitted in a superposed manner on the basis of thecontention zone of FIG. 18. A single user may transmit acontention-based resource that can be utilized in a given contentionzone through a single layer (using a single contention resource) ormultiple layers (using multiple contention resources). Herein, thecontention-based resource may be configured with FDM, TDM, CDM, or thelike.

Each layer may be classified into a base layer and an enhanced layer byassuming a hierarchical layer. The base layer may assume a low ratecoding rate and/or a low modulation order, and the enhanced layer mayassume a high rate coding rate and/or a high modulation order.Therefore, the base layer has a high detection (or decoding) successrate with respect to contention-based transmission, and the enhancedlayer has a relatively low detection (or decoding) success rate withrespect to contention-based transmission. A block diagram oftransmission (Tx)/reception (Rx) for the NOMA scheme to which thehierarchical coding/modulation is applied may be as shown in FIG. 20.

Referring to FIG. 20, each user (UE 1, . . . , UE k) performs base layertransmission and enhancement layer transmission through two Tx chains (aTx chain of the base layer and a Tx chain of the enhanced layer).

Herein, the base layer uses a UE specific spreading code by using a lowcoding rate and/or a low modulation order. For example, the UE 1configures the base layer by using a UE 1 specific spreading code 1.

The enhancement layer uses the UE specific spreading code by using ahigh coding rate and/or a high modulation order. For example, the UE 1configures the enhancement layer by using a UE 1 specific spreading code2. The UE 1 specific spreading code 1 and the UE 1 specific spreadingcode 2 are different from each other.

In the above case, a codeword for the base layer and the enhancementlayer may be predefined. The aforementioned spreading code may beincluded in a predefined codeword. For example, it may be predefinedsuch that, if the number of all codewords (all codewords included in acodebook) is 8, codeword indices 1 to 4 are used for the base layer, andcodeword indices 5 to 8 are used for the enhancement layer.Alternatively, the codeword index may be predefined by being tied to acode rate for each user. The above example is summarized as shown inTable 3 below.

TABLE 3 Layer Code rate Codeword Index Base Layer 1/8 1, 3 1/4 2, 4Enhancement Layer 1/3 5, 7 1/2 6, 8

Since a loop up table of Table 3 above is agreed in advance, a BS mayestimate a code rate on the basis of a codeword index when performingblind detection. By recognizing the base layer, the BS may select alayer to be preferentially selected when performing SIC. For example,upon detecting a signal received from a UE, if a codeword index is 1,the BS may estimate that a code rate is 1/8, and may recognize that thesignal has been transmitted through the base layer. Therefore, the BSmay preferentially decode the base layer when performing SIC.

In addition to the code rate exemplified above, a modulation and codingscheme (MCS) may be related to a codeword index of the baselayer/enhancement layer as shown in Table 3.

In addition, the BS may predefine or broadcast an MCS set to be used inthe base layer and the enhancement layer to all UEs. For example, it maybe restricted such that the base layer uses MCSs 0 to 4, and theenhancement layer uses MCSs 5 to 31. A moving average (MA) signatureincluding the remaining codewords may be randomly selected by the UEs.

Hereinafter, a case where a single user has access in one contentionzone and a case where multiple users have access in one contention zoneare described separately.

(1) Single UE Transmission Case in a Contention Zone

Herein, single user access is assumed in one contention zone. A singleuser achieves a low data rate through a base layer and a high data ratethrough an enhancement layer, when the aforementioned multi-layertransmission is performed. The base layer can achieve a high detectionsuccess rate on the basis of only a channel estimation and decodingprocess. Then, channel estimation performance is improved for theenhancement layer transmitted on the same resource in a superposedmanner on the basis of decoded data of the base layer. Herein, as aknown sequence, the decoded data of the base layer may be reused inchannel estimation for decoding of the enhancement layer. Decodingperformance for the enhancement layer may be improved on the basis ofthe improved channel estimation performance.

(2) Multiple UE Transmission Case in a Contention Zone

Herein, multi-user access is assumed in one contention zone. Forconvenience of explanation, two users A and B are assumed. Each usertransmits a base layer assuming a low rate coding rate and/or a lowmodulation order and an enhancement layer assuming a high rate codingrate and/or a high modulation order in a superposed manner as mentionedin (1) above. Therefore, the base layer and enhancement layer of eachuser is transmitted in a receiving end (BS), and thus at least fourlayers are received in a superposed manner. As mentioned above, the baselayer has a high detection (or decoding) success rate with respect tocontention-based transmission, and the enhancement layer has arelatively low detection (or decoding) success rate with respect tocontention-based transmission. Therefore, as mentioned in (1) above, onthe basis of the high detection (or decoding) success rate of the baselayer, the decoded data of the base layer is utilized as a knownsequence to improve the decoding (or detection) success rate of theenhancement layer. However, since multiple users performcontention-based transmission in one contention zone, collision mayoccur for the same contention resource. Therefore, this can besummarized by the following four cases

Herein, it is assumed that each user has the same resource and powerallocation for the base layer and enhancement layer, and is around thesame geometry area. In addition, it is assumed that the base layer has alow data rate or transmission block size allocation rate (rate_1), sothat it can be decoded at a low signal to interference plus noise ratio(SINR). It is also assumed that the enhancement layer has a high datarate or transmission block size allocation rate (rate_2), so that it canbe decoded at a high SINR. Herein, if multiple users have differentgeometries, each user may transmit only a single layer (only a baselayer) or may transmit all of multiple layers according to an SINR valuebased on the geometry.

1) When only a user 1 attempts with probability of p and a user 2 muteswith probability 1−p, an achievable data rate is rate_1+rate_2 and thusthe average system data rate by only the user 1 isp*(1−p)*(rate_1+rate_2).

2) When only the user 2 attempts with probability of p and the user 1mutes with probability 1−p, the achievable data rate is rate_1+rate_2and thus the average system data rate by only the user 2 isp*(1−p)*(rate_1+rate_2).

3) When both the user 1 and the user 2 attempt with probability of p,each achievable data rate is rate_1 and thus the average system datarate by the user 1 and user 2 is p*p*(rate_1+rate_1).

4) When both the user 1 and the user 2 mute with probability of 1−p,each achievable data rate is 0 and thus the average system data rate is(1−p)*(1−p)*0.

So, the overall average system datarate=2*p*(1−p)*(rate_1+rate_2)+2*p*p*(rate_1). In the analysis above,the rate_1 and rate_2 of the two users may be different according to asuperposition scheme, a resource allocation scheme, and a powerallocation scheme, and a higher overall average system data rate can beachieved through optimization. In addition, due to a geometry differenceof the two users, there may be a difference in an overall average systemdata rate that can be achieved. In addition, when N users performcontention on the same contention resource in the same contention zone,it may be extendedly applied as follows:comb(N,1)*p*(1−p)^(N−1)*(rate_1+rate_2)+comb(N,2)*p^2*(1−p)^(N−2)*(2*rate_1).

On the basis of the analysis above, a hierarchical coding/modulationscheme in contention based transmission may be utilized in channelestimation of an enhancement layer, repetition of the enhancement layer,retransmission for previous transmission, or the like as describedbelow.

As mentioned in (1) above, on the basis of the high detection (ordecoding) success rate for the base layer of each user, the decoded dataof the base layer of each user may be utilized as the known sequence toimprove the decoding (or detection) success rate of the enhancementlayer of each user.

The enhancement layer can transmit more data bits than those of the baselayer. Therefore, some data bits (or all data bits) of the enhancementlayer of each user may be utilized as enhanced redundancy bits.

Herein, the enhanced redundancy bits may be utilized with a low rate orrepetition for a high decoding (or detection) success rate of theenhancement layer, and may be utilized for detection or decodingperformance of the base layer.

Herein, the enhanced redundancy bits may be utilized as enhancedredundancy bits for additional data transmission with respect to thebase layer, and may be utilized as encoded CRC bits with respect to thebase layer.

In previous transmission, redundancy bits of the enhancement layer forcurrent transmission may be utilized for retransmission with respect tofailed transmission of the base layer. The operation above may beperformed after receiving NACK in HARQ. Irrespective of an HARQoperation, a redundancy bit of the enhancement layer may be usedstatically to retransmit the base layer of the previous transmission. Itcan be expected that a collision probability is decreased with twotransmission attempts according to user traffic generation. Herein,since high data rate transmission may be possible in the enhancementlayer, the operation may be performed in every transmission, orretransmission of the base layer may be collectively performed forseveral previous transmission attempts periodically according to aspecific value.

The base layer may perform transmission by containing information(C-RNTI, etc.) for a UE identification, and the enhancement layer maytransmit traffic data of the UE, thereby switching to an HARQ processoror grant-based transmission through the UE identification. If the BS hasdetected the UE identification but fails in data detection, since the BScan know which UE transmits data through the UE identification, dataretransmission may be requested to the UE which has transmitted thedata. If the UE retransmits the data, the BS may combine and decode theprevious UE identification of the base layer and the retransmitted dataof the enhancement layer. Herein, the UE identification and the data aretransmitted through different layers in one data channel (e.g., PUSCH).

In an environment where the number of DMRSs is less than the number ofcodewords, the base layer and enhancement layer for one user are tied toone DMRS. Therefore, two codewords (respectively for the base layer andthe enhancement layer) may be used with one DMRS. Since the base layerand the enhancement layer are transmitted by a single user in asuperposed manner in all of the above operations, channel estimation maybe performed through one reference signal. Accordingly, even if thenumber of reference signals is less than the number of codewords,channel equalization and MUD may be performed in a receiving end.

For example, it is assumed that the number of DMRSs is 4, and the numberof codewords is 8. In addition, it is assumed that the DMRSs areorthogonal to each other in order to effectively perform channelestimation. Since contention-based data transmitted from multiple usersis identified with the DMRS, channel estimation performance hasconventionally been determined according to the number of DMRSs even ifthe number of codewords is greater than the number of DMRSs. Therefore,MUD performance has not been ensured. However, even if the number ofcodewords is greater than the number of DMRSs, in a case where the baselayer and enhancement layer for one user are tied to one DMRS, 8 layerscan be identified when the number of DMRSs is 4. Therefore, there is anadvantage in that the number of available codewords can be moreincreased. That is, it is possible to support 1:M mapping between theDMRS and the codeword index. Herein, M is the number of spreadingcodewords corresponding to one DMRS.

A relation of 1:M mapping between the DMRS and the codeword index may bepre-defined, or may be informed through RRC signaling or broadcasting orthe like using a common control channel. For example, codeword selectionsatisfies the following relation:DMRS_INDEX=┌(Codeword_INDEX)/M┐(=ceil(Codeword_INDEX/M)). Herein,M=(Maximum Codeword_INDEX)/(Maximum DMRS_INDEX). For example, if themaximum number of codewords is 8 and the maximum number of DMRSs is 4,according to DMRS_INDEX, Codeword_INDEX is 1 or 2 when DMRS_INDEX is 1,and Codeword_INDEX is 3 or 4 when DMRS_INDEX is 2.

In all of the aforementioned operations, the base layer and theenhancement layer may have different power allocation. When a totalpower constraint of the UE is fixed to A, it is configured such that asum of power B of the base layer and power C of the enhancement layer isC (A=B+C). Accordingly, channel equalization is performed based on thepower allocation also in channel equalization of the receiving end.Basically, power allocation of each of the base layer and theenhancement layer may be evenly allocated with A/2, and may becontrolled by the BS if power allocation of the base layer and theenhancement layer is performed with a different power ratio. In thiscase, control information from the BS to the UE may be indicated throughRRC level signaling, high layer information, or common controlinformation. That is, power allocation of the base layer and theenhancement layer may be signaled from the BS to the UE.

FIG. 21 is a flowchart showing a procedure of transmittingcontention-based data by applying HM according to an embodiment of thepresent specification.

First, a contention-based resource may correspond to a resource regionfor contention-based uplink connection or uplink data transmission onthe basis of non-orthogonal multiple access

In step S2110, a UE receives, from a BS, information regarding apre-defined codeword for non-orthogonal multiple access. The pre-definedcodeword includes a first spreading code and a second spreading code.The pre-defined codeword may correspond to all codewords included in acodebook pre-defined between the BS and the UE. Therefore, both of thefirst spreading code and the second spreading code may correspond to thecodeword.

In step S2120, the UE configures a base layer by using the firstspreading code, and configures an enhancement layer by using the secondspreading code.

In step S2130, the UE transmits a UE identification and data to the BSthrough a contention-based resource which uses the base layer and theenhancement layer in a superposed manner. In this case, the UEidentification is transmitted through the base layer, and the data istransmitted through the enhancement layer. In addition, the UEidentification and the data are transmitted through the same datachannel. The UE identification and the data may be transmitted only withthe data channel without having to distinguish a control channel and thedata channel, each of which has different reliability.

That is, in the present embodiment, one user (or UE) performscontention-based transmission by superposing two layers (a base layerand an enhancement layer) in a wireless communication system to which anon-orthogonal multiple access scheme is applied. Since the base layerand the enhancement layer are identified with a codeword, acontention-based resource may be identified with the base layer and theenhancement layer according to the codeword.

The BS may perform multi-user detection (MUD) for the data and the UEidentification transmitted by the UE. If the BS succeeds in detection ofthe UE identification and fails in detection of the data, the UE mayreceive a retransmission request for the data from the BS. Sincedetection of the UE identification is successful, the BS can recognizewhich UE transmits the data, and thus data retransmission can berequested to a corresponding UE. The UE may retransmit the data to theBS through the enhancement layer. In this case, the UE identificationand the data retransmitted from the UE may be decoded by being combinedto each other. Without having to retransmit the UE identification, theBS may decode the UE identification by combining the retransmitted dataand the UE identification previously transmitted through the base layer.

In addition, the UE may transmit a reference signal for channelestimation to the BS. In this case, the number of reference signals isless than the number of pre-defined codewords. In addition, it may beconfigured such that the base layer and enhancement layer which are usedin a superposed manner may correspond to one reference signal. Thereference signal may correspond to a DMRS.

Conventionally, since contention-based data transmitted from multipleusers is identified with the DMRS, it has been meaningless even if thenumber of codewords is greater than the number of DMRSs. However, if thebase layer and enhancement layer for one user are tied to one DMRS, twocodewords can be used with one DMRS. Therefore, even if the number ofcodewords is greater than the number of DMRSs, it is possible toidentify more layers than the number of DMRSs.

In addition, the UE may receive power allocation information for thebase layer and the enhancement layer from the BS through radio resourcecontrol (RRC) signaling, high layer signaling, or common controlinformation. Accordingly, the BS performs channel equalization on thebasis of the power allocation information for each layer.

A code rate for the base layer and a code rate for the enhancement layermay be designated according to a codeword index of the predefinedcodeword. Alternatively, modulation and coding scheme (MCS) for the baselayer and MCS for the enhancement layer may be designated according tothe codeword index of the predefined codeword.

That is, a relation between the codeword for the base layer/enhancementlayer and the codeword index and a relation between the MCS for the baselayer/enhancement layer and the codeword index are broadcast to all UEslocated in a cell in a look up table manner. The codeword index may bepre-defined by being tied to the codeword for each user. Therefore, theBS may estimate a code rate on the basis of a codeword index whenperforming blind detection. By recognizing the base layer, the BS mayselect a layer to be preferentially selected when performing SIC.

Although it is exemplified above that the invention is applied when aspreading codeword to be decoded based on SIC in a receiving end isapplied to the base layer and the enhancement layer, the invention mayalso be equally applied to a spreading codeword or codebook scheme inwhich decoding is performed through ML, MPA, or the like in thereceiving end. For example, when a single user can use two or morelayers by identifying the layers according to signal strength (power),codeword, codebook, interleaver, or the like, one layer may be appliedas the base layer and the other one or more layers may be applied as theenhancement layer to obtain the same effect. In this case, a decodingrate of each layer may be controlled by hierarchically applying thesignal strength or the code rate.

For convenience of explanation, the invention is described above bytaking an example in which a ratio of the base layers and theenhancement layers is 1:1 from a single user perspective and thus twolayers exist. However, the same effect can also be obtained in anenvironment where a plurality of base layers and enhancement layersexist. For example, a ratio of the base layers and the enhancementlayers is N:L from a single user perspective and thus that (N+L) layersexist. In order to support a high decoding rate, a low modulation orderand/or low code rate may be applied to N base layers to support a highdecoding rate, and a relatively high modulation order and/or high coderate may be applied to L enhancement layers.

FIG. 22 is a block diagram showing an apparatus for wirelesscommunication for implementing an embodiment of the present invention.

An apparatus 2200 for wireless communication includes a processor 2210,a memory 2220 and a radio frequency (RF) unit 2230.

The processor 2210 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 2210. Theprocessor 2210 may handle a procedure explained above. The memory 2220is operatively coupled with the processor 2210, and the RF unit 2230 isoperatively coupled with the processor 2210.

The processor 2210 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememory 2220 may include read-only memory (ROM), random access memory(RAM), flash memory, memory card, storage medium and/or other storagedevice. The RF unit 2230 may include baseband circuitry to process radiofrequency signals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memory 2220 and executed byprocessor 2210. The memory 2220 can be implemented within the processor2210 or external to the processor 2210 in which case those can becommunicatively coupled to the processor 2210 via various means as isknown in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for transmitting, by a user equipment(UE), contention-based data in a wireless communication system to whicha non-orthogonal multiple access scheme is applied, the methodcomprising: receiving, from a base station, information regarding apredefined codeword for non-orthogonal multiple access, wherein thepredefined codeword comprises a first spreading code and a secondspreading code; configuring a base layer by using the first spreadingcode, and configuring an enhancement layer by using the second spreadingcode; transmitting, to the base station, a UE identification and datathrough a contention-based resource which uses the base layer and theenhancement layer in a superposed manner; receiving, from the basestation, a retransmission request for the data if the base stationsucceeds in detection of the UE identification and fails in detection ofthe data; and retransmitting, to the base station, the data through theenhancement layer, wherein the UE identification is transmitted throughthe base layer, and wherein the data is transmitted through theenhancement layer.
 2. The method of claim 1, wherein the UEidentification and the data are transmitted through the same datachannel.
 3. The method of claim 1, further comprising transmitting, tothe base station, a reference signal for channel estimation, wherein thenumber of reference signals is less than the number of the predefinedcodewords, and wherein the base layer and the enhancement layer whichare used in a superimposed manner are configured to correspond to onereference signal.
 4. The method of claim 1, further comprisingreceiving, from the base station, power allocation information for thebase layer and the enhancement layer through radio resource control(RRC) signaling, high layer signaling, or common control information. 5.The method of claim 1, wherein a code rate for the base layer and a coderate for the enhancement layer are designated according to a codewordindex of the predefined codeword, or wherein modulation and codingscheme (MCS) for the base layer and MCS for the enhancement layer aredesignated according to the codeword index of the predefined codeword.6. A UE for transmitting contention-based data in a wirelesscommunication system to which an non-orthogonal multiple access schemeis applied, the UE comprising: a transceiver that transmits and receivesa radio signal; and a processor operatively coupled to the transceiver,wherein the processor is configured to: receive, from a base station,information regarding a predefined codeword for non-orthogonal multipleaccess, wherein the predefined codeword comprises a first spreading codeand a second spreading code; configure a base layer by using the firstspreading code, and configure an enhancement layer by using the secondspreading code; transmit, to the base station, a UE identification anddata through a contention-based resource which uses the base layer andthe enhancement layer in a superposed manner; receive, from the basestation, a retransmission request for the data if the base stationsucceeds in detection of the UE identification and fails in detection ofthe data; and retransmit, to the base station, the data through theenhancement layer, wherein the UE identification is transmitted throughthe base layer, and wherein the data is transmitted through theenhancement layer.
 7. A method for transmitting, by a base station,contention-based data in a wireless communication system to which anon-orthogonal multiple access scheme is applied, the method comprising:transmitting information regarding a predefined codeword fornon-orthogonal multiple access to a user equipment (UE), wherein thepredefined codeword comprises a first spreading code and a secondspreading code; receiving, from the UE, a UE identification and datathrough a contention-based resource which uses the base layer and theenhancement layer in a superposed manner; transmitting a retransmissionrequest for the data from the base station if detection of the UEidentification is successful and detection of the data fails; andreceiving data retransmitted from the UE through the enhancement layer,wherein the base layer is configured by using the first spreading code,and the enhancement layer is configured by using the second spreadingcode, wherein the UE identification is received through the base layer;and wherein the data is received through the enhancement layer.
 8. Themethod of claim 7, wherein the UE identification and the data arereceived through the same data channel.
 9. The method of claim 7,further comprising: performing multi-user detection (MUD) for the dataand the UE identification; wherein the UE identification and the dataretransmitted from the UE are decoded by being combined to each other.10. The method of claim 7, further comprising receiving a referencesignal for channel estimation from the base station, wherein the numberof reference signals is less than the number of pre-defined codewords,and wherein the base layer and enhancement layer which are used in asuperposed manner are configured to correspond to one reference signal.11. The method of claim 7, further comprising transmitting powerallocation information for the base layer and the enhancement layer tothe UE through radio resource control (RRC) signaling, high layersignaling, or common control information.
 12. The method of claim 7,wherein a code rate for the base layer and a code rate for theenhancement layer are designated according to a codeword index of thepredefined codeword, or wherein modulation and coding scheme (MCS) forthe base layer and MCS for the enhancement layer are designatedaccording to the codeword index of the predefined codeword.